A locking type pushbutton switch of this kind is represented in FIG. 1. In FIG. 1, an upper case 1 has an open lower end closed by a lower case 2, and a stem 3 is provided to move vertically through the upper wall 1a of the upper case 1. At the upper end of this stem 3, a pushbutton not shown is mounted. A spring 4 is provided between the stem 3 and the upper surface of upper case 1 so as to urge the stem 3 upwardly.
On opposite surfaces of the inner wall of upper case 1, grooves 1b and 1b are formed as shown in FIG. 2. A fixed plate 5 shown in FIG. 3 is inserted into the grooves 1b and 1b of the upper case 1 and fixed therein by attaching the lower case 2 to the upper case 1. A hole 6 is bored at the center of this fixed plate 5 and the one end 7a of a C-shaped lock pin 7 is engaged within this hole 6. The other end 7b of this lock pin 7 is inserted into a heart-shaped cam groove 8 of the stem 3 and is held in resilient contact with the bottom part of the heart-shaped cam groove 8 by a plate spring 9 provided between the lock pin 7 and the inner wall of upper case 1.
Moreover, the lower case 2 is provided with the terminals 10 and 11 projected downwards. Terminal 10 is integrally provided with a fixed contact 10a having a projection 10b, while the terminal 11 is provided with a movable contact 11a. Moreover, the fixed contact 10a is held within a fixed resin frame 12. This frame 12 is integrally provided with the flexible tongue piece 12a, and a fixed plate spring 14 is fitted over the top portion of the frame 12 to press the flexible piece 12a rightwardly in FIG. 1 when the stem 3 is depressed into the case 1.
In such a locking type pushbutton switch, when the pushbutton (not shown) is depressed downward, causing the stem 3 to move downwardly in opposition to the spring force of the spring 4, the plate spring 14 and flexible piece 12a are bent to the right in FIG. 1 and the movable contact 11a is placed in contact with the projection part 10b of the fixed contact 10a. Moreover, at this time, the end 7b of lock pin 7 slidingly moves within the heart-shaped cam groove 8 of the stem 3. After the movable contact 11a is in contact with the projection part 10b, namely when the movable contact 11a closes, the stem 3 is locked by the lock pin 7 and heart-shaped cam groove 8 so the stem cannot move upwards. When the pushbutton is further depressed from such a condition and is then released, the locking engagement of the lock pin in the cam groove is released and the stem 3 is returned to the initial state by a spring force of the spring 4, and the movable contact 11a opens. Under this condition, a stepped part (not shown) of the stem 3 is in contact with the upper wall of the upper case 1 and thereby the stem 3 is prevented from moving further upwards as a result of the spring force of the spring 4.
A locking type pushbutton switch having such structure is required to have a simple structure with less number of parts, to be more tolerant of dimensional errors and assure easy manufacturing and long operating life.